Method and system for fuel vapor control

Abstract

Methods and systems are provided for reducing fuel vapor generation from a fuel tank in a hybrid vehicle. A layer of gel-foam fire retardant is layered over the surface of fuel in the fuel tank. In response to the layer being below a fuel level in the fuel tank, fuel pump operation may be automatically disabled.

The invention claimed is: 
     
       1. A method for a vehicle fuel system, comprising floating a layer of gel-foam fire retardant on a surface of liquid fuel in a fuel tank to reduce an amount of fuel vapors generated in a dome region of the fuel tank, the vehicle being an on-road vehicle wherein the fuel system includes a fuel level sensor coupled to the layer of gel-foam fire retardant for indicating a position of the layer in the fuel tank. 
     
     
       2. The method of  claim 1 , wherein the fuel system further includes a fuel pump coupled in the fuel tank, the method further comprising, disabling operation of the fuel pump in response to the position of the layer being lower than a threshold position. 
     
     
       3. The method of  claim 2 , wherein the threshold position is based on a road incline, the threshold position being higher as the vehicle travels on a higher incline. 
     
     
       4. A method for a vehicle fuel system, comprising:
 adjusting operation of a fuel pump based on a position of a layer of gel-foam fire retardant in a fuel tank, the layer floating on a surface of fuel in the fuel tank. 
 
     
     
       5. The method of  claim 4 , wherein the adjusting includes enabling operation of the fuel pump when the layer is above a threshold position and disabling operation of the fuel pump when the layer is below the threshold position. 
     
     
       6. The method of  claim 5 , wherein the threshold position is based on one or more of a road incline, vehicle acceleration/deceleration, vehicle lateral acceleration, steering wheel angle, and vehicle yaw. 
     
     
       7. The method of  claim 6 , wherein the fuel pump is located within a depression at a bottom of the fuel tank. 
     
     
       8. The method of  claim 4 , wherein fuel tank vapors are stored in a fuel system canister coupled to the fuel tank, the method further comprising, indicating degradation of the layer based on a purging frequency of the fuel system canister. 
     
     
       9. The method of  claim 8 , wherein the indicating includes, in response to the purging frequency of the fuel system canister over a vehicle drive cycle being higher than a threshold rate while no fuel sloshing is detected, indicating degradation of the layer of gel-foam fire retardant; and in response to the purging frequency of the fuel system canister over the vehicle drive cycle being higher than the threshold rate while fuel sloshing is detected, indicating no degradation of the layer of gel-foam fire retardant. 
     
     
       10. The method of  claim 9 , further comprising, in response to the indication of degradation of the layer of gel-foam fire retardant, increasing engine an operation time to enable increased canister purge frequency. 
     
     
       11. The method of  claim 10 , wherein fuel sloshing is determined based on a vehicle accelerometer and/or a vehicle navigation system. 
     
     
       12. A fuel system coupled to a vehicle, comprising: a fuel tank for storing a liquid fuel; a fuel pump coupled in the fuel tank for delivering fuel to an injector; and a layer of gel-foam fire retardant floating on a surface of the liquid fuel in the fuel tank, a fuel level sensor coupled to the layer of gel-foam fire retardant for indicating a position of the layer within the fuel tank. 
     
     
       13. The system of  claim 12 , further comprising, a controller with computer readable instructions for, adjusting an operation of the fuel pump based on the position of the layer within the fuel tank relative to a threshold position. 
     
     
       14. The system of  claim 13 , wherein a bottom surface of the fuel tank includes a depression and wherein the fuel pump is positioned within the fuel tank, on the depression of the bottom surface. 
     
     
       15. The system of  claim 14 , wherein the fuel pump includes a fuel pump inlet configured to receive fuel from the fuel tank and wherein the threshold position is based on a location of the fuel pump inlet. 
     
     
       16. The system of  claim 15 , wherein adjusting the operation of the fuel pump includes, enabling operation of the fuel pump when the position of the layer is above the threshold position and disabling the fuel pump when the position of the layer is below the threshold position. 
     
     
       17. The system of  claim 16 , further comprising a canister coupled to the fuel tank for storing fuel vapors generated in the fuel tank, wherein the controller includes further instructions for intermittently purging fuel vapors from the canister to an engine intake of the vehicle. 
     
     
       18. The system of  claim 17 , wherein the controller includes further instructions for indicating degradation of the layer of gel-foam fire retardant based on a purging frequency of the canister over a vehicle drive cycle.